The present invention relates to a plasma processing apparatus using rotary magnets, particularly for arc discharge processing and for magnetron sputter deposition or etching processes.
High density plasma sources and devices for low pressure plasma processing of surfaces utilize auxiliary magnetic fields. Obviously the magnetic field can be used for magnetic confinement of plasma electrons and ions. The Lorentz force vector F affecting the motions of charged particles is defined as:
F=q(vxc3x97B),
where v is the velocity vector of a charged particle (electron or ion) having charge qe,i, and B is the vector of magnetic induction. The Lorentz force acts on electrons and ions having non-zero vector product (vxc3x97B), i.e. having a velocity component Vnorm (e,i) normal to the vector B. These electrons and ions (of the mass me,i) are forced to gyrate around the magnetic flux lines at Larmor radii defined as
re,i=Vnorm(e,i)me.i/qe,iB.
The most typical driving force for charged particles is the electric field (vector E). In this case the resulting flows of particles have a direction (drift) given by the vector product (Exc3x97B). Note that the higher the particle velocity (energy) is, which depends on the field E, on collisions, etc., the higher the magnetic induction B must be to maintain the same Larmor radius. The higher the induction B is the lower Larmor radius of particles. These relations are very important, because the magnetic confinement can be effective only in cases where the reactor chamber dimensions are larger than the Larmor radii of particles. Otherwise the particles recombine at the chamber walls. In strong magnetic fields the Larmor radii are short and the plasma can be confined in small volumes. Due to reduced recombination losses the magnetic confinement leads to more dense plasmas compared with cases without magnetic means. At low gas pressures where the collisions between particles are less frequent the mean free paths of particles usually are longer than the dimensions of reactor chambers. The particles can gain high energy from generating fields and the wall recombination rate can prevail ionization. Such a plasma can not sustain without an additional magnetic confinement.
A magnetic field can be used also as an active component in different mechanisms of plasma generation. For example in electron and ion cyclotron resonances (ECR, ICR) where magnetic induction B relates to both the generator frequency as and the electron or ion mass:
B=xcfx89me,i/qe,i.
Other examples are hybrid resonances, Landau damping-assisted heating of the plasma, etc. At both an optimal value of the magnetic induction and an optimal shape of the magnetic flux the resonant generation of the high density plasma can be combined with its confinement in a defined volume.
A wide variety of magnetic confinements (plasma traps) for the radio frequency (RF) glow discharges using static magnetic fields generated by electromagnetic coils were patented by A. S. Penfold and J. A. Thornton (U.S. Pat. No. 4,116,794 dated 26-09-1978). The patent introduces different arrangements of magnetic coils optimized for different geometries of RF electrodes. The aim of this optimization is to maximize the confinement of the discharge and its sustainment down to low gas pressures in the discharge chamber. All the coil arrangements claimed are static both in time and space.
It is also possible to xe2x80x9cmovexe2x80x9d the magnetic field in the space either by moving, the magnetic coil itself or step-by-step switching on the current to coils, configuring an array of coils. For example the moving-coil magnetic field was used in the microwave ECR discharges (R. Hytry et al., J. Vac. Sci. Technol., 1993). The periodic replacement of the field in a static system of electromagnets by successive shifting of the generation current in the respective coils was reported in an inductive RF discharge by M. Murata et at. (Vacuum 1997). These movements of the magnetic field are based on spatial replacement of the magnetic means without change of shapes of magnetic flux lines and field geometry.
Generally the design of proper shape of the magnetic field with electromagnetic coils is impossible in cases when high magnetic induction is required in small volumes or restricted areas. Regarding these problems 1984 was a year of breakthrough when a discovery was made on strong permanent magnets based on ternary inter-metallic compounds, e.g., Ndxe2x80x94Fexe2x80x94B (e.g. see book xe2x80x9cFerromagnetic materialsxe2x80x9d by E. P. Wohlfarth and K. H. J. Buschow, North-Holland 1988, Chapter 1, FIG. 1 p.4 and p.7). This kind of magnets can provide a very strong magnetic field (more than 0.1 T at the magnet surface). In many practical cases these magnets successfully replace electromagnetic coils and allow magnetic field applications with well defined shapes in a selected space. The most important possibility is forming of intense local magnetic fields with a proper design of magnetic flux lines, which is not practically possible with coils.
A local magnetic field was used in apparatus for generation of a linear arc discharge for plasma processing (LAD) by L. Bardos and H. Barankova (Swedish patent publication SE 503 141, Nov. 1994), particularly for processing on surfaces of solid substrates. In this apparatus a pair of electrode plates placed opposite to each other and connected to the same pole of the generator are positioned in a magnetic field produced by magnets for development of linear hot zones on the electrode plates where an arc discharge is generated. The electrode plates form a parallel-plate hollow cathode, negative with respect to the surrounding plasma, which represents a virtual anode. The hot zones are formed due to an ion bombardment of the plate surfaces in the hollow cathode discharge between the plates. The magnetic field perpendicular to the cathode plates in this apparatus facilitates the hollow cathode discharge in the slit between the plates. The position of magnets can be tuned with respect to the electrode plates by a tuner and the distribution of the magnetic field is tuned by magnets and by additional magnets. Thus, the magnetic field used in the LAD source is stationary both in space and time. For selected parameters of gas flow rate, generation power, gas pressure etc., the magnetic field can be tuned and optimized for uniform distribution of the resulting plasma density along the slit. However, due to non-zero vxc3x97B force in many practical applications the ions tend to concentrate more at one side of the hollow cathode slit. Time dependent changes of discharge parameters during operation of LAD source can cause changes of both the particle velocities and distribution of electric fields in the discharge. This can result in a non-uniform erosion of the cathode material by the arc sputtering and/or evaporation and consequently in a non-uniform processing rate on the substrates.
Another example of utilization of strong permanent magnets is the well-known magnetron sputtering/sputter etching device. Principles and performances of different magnetron systems for sputter etching/deposition processes are described in a number of works. Regardless of both their almost xe2x80x9cclassicalxe2x80x9d concept and their commercial availability since 1976, the magnetrons still undergo construction changes. Reasons for this are either an unsatisfactory plasma density at the substrate for selected applications or ineffective and non-uniform magnetron target utilization accompanied by a small erosion area on the target during sputtering. The former problem can be solved partly by xe2x80x9cunbalancingxe2x80x9d (opening) of the magnetic flux lines which allows an expansion of the plasma towards the substrate (B. Window and N. Savvides in 1986), or by an additional ionization tool, for instance by a hollow cathode (J. J. Cuomo et aL, U.S. Pat. No. 4,588,490 filed 22-05-1985), alternatively by an auxiliary RF coil (S. M. Rossnagel and J. Hopwood, Appl. Phys. Lett., 1993). The later problem is reduced in magnetrons with a rotatable cylindrical target xe2x80x9cC-Magxe2x80x9d (M. Wright et al, J. Vac. Sci. Technol., 1986; A. Belkind et al., Thin Solid Films 1991) and in hollow target magnetrons (disclosed in U.S. Pat. No. 5,073,245 by V. L. Hedgcoth, 1991). A movement of the target with respect to the magnetic field can be substituted by a shifting of the magnetic field under the target. This is described in European Patent Application EP-B1-0 603 587 (Balzers AG, 1992), in which the system of permanent magnets, forming a tunnel-like magnetic field, is being laterally displaced under the target. The magnet poles can be pivoted and synchronized with the lateral shift to extend the lateral displacement of the tunnel-like field thereby to enlarge the erosion of the target. Another solution is based on new designs of magnetic fields using permanent magnets as disclosed in U.S. Pat. No. 5,262,028 by Sierra Applied Sciences, Inc. A review about different arrangements of magnetic fields in all known magnetrons was presented for example by J. Musil et al. (Vacuum, 1995) or by R. Kukla (Surf. Coat. Technol., 1997). In all the magnetrons either the stationary magnetic field is used (closed or unbalanced) or the field is moving during the processing with respect to the target (e.g. C-Mag), but without substantial change of its shape. The sputtering regimes are therefore xe2x80x9cprescribedxe2x80x9d.
An object of present invention is therefore to overcome the drawbacks of the above described prior art techniques and to provide a plasma processing apparatus with rotary magnets for obtaining an adjustable time variable magnetic field.
In a first aspect according to the present invention, a plasma processing apparatus comprising means for generating a plasma discharge, and means for confining the plasma in a magnetic field, comprises at least one pair of a first rotary permanent magnet system and a second rotary permanent magnet system placed opposite to each other, comprising individual permanent magnets having maximum magnetic induction more than 10xe2x88x921 Tesla, a driver system disposed for the driving motion of said rotary permanent magnet systems, a basic plasma processing device used in combination with said rotary permanent magnet systems to form time variable magnetic flux lines and to affect a plasma produced by said basic plasma processing device, and a control system comprising a sensor system and a feedback system connected to said driver system, disposed for control of motions of said rotary permanent magnet systems with respect to changes of said plasma.
In a second aspect according to the present invention a plasma processing apparatus, comprising means for generating a plasma discharge, and means for confining the plasma in a magnetic field, comprises at least one pair of a first rotary permanent magnet system and a second rotary permanent magnet system placed opposite to each other, comprising individual permanent magnets having maximum magnetic induction more than 10xe2x88x921 Tesla, a driver system disposed for the driving motion of said rotary permanent magnet systems, a basic plasma processing device comprising a linear arc discharge apparatus with at least one pair of hollow cathode plates placed in a magnetic field where stationary magnetic flux lines are either replaced or affected by time variable magnetic flux lines produced by said rotary permanent magnet systems for generation of a time dependent hollow cathode plasma, and a control system comprising a sensor system and a feedback system in connection with said driver system disposed for control of motions of said rotary permanent magnet systems with respect to changes of said time dependent hollow cathode plasma.
In a third aspect according to the present invention the basic plasma processing device comprises a magnetron device having a stationary magnet system, wherein the rotary permanent magnet systems are disposed to form time variable magnetic flux lines which traverse a magnetron target for generation of a time dependent magnetron plasma.
In a fourth aspect according to the present invention the basic plasma processing device comprises a magnetron device with rotatable magnetron target wherein said rotary permanent magnet systems are installed on a holder together with the stationary magnet system.
In a fifth aspect according to the present invention the basic plasma processing device comprises an active plasma in a reactor, where the rotary permanent magnet systems are disposed outside and/or inside the reactor to form time variable magnetic flux lines and to generate time dependent dense plasma regions.
In a sixth aspect according to the present invention said rotary permanent magnet systems comprise individual permanent magnets having different maximum magnetic inductions and/or different directions of magnetic flux lines.
In a seventh aspect according to the present invention said driver system controlled by the control system enables driving of the rotary permanent magnet systems in a step-wise motion or a vibrational motion around selected positions.